The invention generally relates to a manual hammer tacker for striking a procession of inventive fasteners or tacks on a repetitive and highly efficient basis. Such tacks are characterized by, among other things, a broad flat head that is particularly effective for fastening soft, thin, membrane materials, such as vapor wraps like Tyvek®. In accordance with the present invention, the hammer tacker disclosed herein is particularly improved for more dependable and reliable operability, especially on vertical surfaces in contrast to flat or gently sloping surfaces.
The hammer tacker in accordance with the present invention is the culmination to date of a development project extending back over time that included several prototype versions, two of which are disclosed in commonly-owned U.S. Pat. No. 5,927,922, entitled “Tack, Hammer Tacker Therefor, and Method,” the disclosure of which is incorporated fully herein by this reference. A third prototype version is disclosed in connection with FIGS. 1-3 hereof. These three prototype versions form a thread of design strategy which has been significantly abandoned in favor of the hammer tacker in accordance with the present invention.
The first version in this thread of three is shown and described in connection with FIGS. 2-5 as well as 10a-15b of U.S. Pat. No. 5,927,922; the second version in connection with FIGS. 16-18 of U.S. Pat. No. 5,927,922. All three of the prototype versions are either more particularly described in (or can be sufficiently “particularly” reckoned by reference to) U.S. Pat. No. 5,927,922.
These three prototype versions essentially share the following characteristics. They all utilize a “double parallelogram” leaf spring as the main workhorse for the tack-driving mechanism. Also, they all utilize a tack-feeding mechanism that reaches around from an origin above the tack heads to push the tacks by contact underneath their heads, and thus by their legs (or more accurately, shanks). As an aside, the previous reference directions “above” and “underneath” are referenced relative to the tacks' heads and shanks merely for convenience in this description and otherwise do not limit the use of the hammer tacker to any particular orientation, even upside down if possible, as against a ceiling.
Versions two and three of the prototypes represent comparable projects of debugging bugs that were found in each's previous iteration. Version three hereof represents the most advanced and comparatively debugged version of this thread. Nevertheless it still retains, or else gave arise to new, bugs which appear to have no simple fixes. Hence, this design thread was sort of abandoned in favor of proceeding a different way, and as in accordance with the invention.
To digress briefly, and dwell on FIGS. 1 through 6, they show the culmination of the final (referred to as the third) version of the prototype versions. FIG. 1 shows a hammer tacker 525, fairly comparable to hammer tacker 25 or 125 in U.S. Pat. No. 5,927,922. FIG. 2 is an enlarged scale perspective view taken in the direction of arrows II-II in FIG. 1, wherein the near-side half of the split housing (preferably produced nowadays from plastic) is removed to reveal the tack driving-and-feed mechanism 540, which includes, in its main aspects, a double parallelogram leaf spring 541, a piston 542 held at the vibrating end of the leaf spring 541, a ram 543 extending down from the piston 542, and a rocker-arm/pawl linkage 544/545 actuated by the piston 542. The rocker arm 544 portion terminates in pawl portion 545. A tack 520 in the lead position (eg., the position in the procession from which the ram discharges a tack on the strike stroke) is shown in broken lines, other tacks 520−n of the strip 570 being shown in broken lines as well in the handle 533's interior feed track 576.
Each of these prototype versions are generally typified by, namely, a double-parallelogram leaf spring (eg., 541 in FIG. 3), and a reach-around rocker-arm/pawl linkage (eg., 544/545 in FIG. 3). The third prototype version described hereby also has a supplemental spring 546 for the rocker-arm/pawl linkage 544/545. There is also a tack-strip hold-down spring 547 (shown pressing at least on the tack 520−n in the next-to-lead position, which immediately succeeds the tack 520 in the lead position). Some of the shortcomings that persist or have arisen in the third version include the following, which are described over the following extended passage.
To begin with, the spring designs are custom, original designs. As such, the spring designs prove challenging to fabricate and nearly impossible to achieve uniformity between one copy to the next. An early design choice was to produce these spring components out of beryllium copper. A factor in favor of this material is its expected longer working life when compared to an equivalent construction out of spring steel.
Nevertheless, regardless if steel or beryllium copper, fabrication of these springs requires layout on and lancing from flat stock, followed by multiple forming steps to produce all the bends and curves. After this, the formed parts have to be heat treated for, among other reasons, returning the material back to serviceable spring material after much degradation thereto occurs through the forming processes. However, industry-specified heat treatments cause distortions, probably in all cases, it being usual that such distortions are readily apparent to by the un-aided eye alone. Hence the parts usually have to be given individual attention after heat treatment to re-tune back to specified dimensional tolerance and performance metrics.
Moreover, each individual custom spring-design is likely overly-complicated in terms of both layout and formation. As for formation especially of the rocker-arm/pawl linkage and its supplemental spring, these involve formation of tricky bends and curves that prove challenging to keep within even a loose dimensional tolerance. As said, dimensional tolerance laxness is only further compounded by a heat treatment that predictably adds distortion. In consequence, it is practically impossible to produce duplicate copies of the same part.
Also, assembly is difficult. FIGS. 2 and 3 shows that the three springs 541, 544/545 and 546 have to be intertwined like a three-dimensional puzzle, and then carefully rested between both halves of the split housing. If the parts as they often do get jarred apart, then a worker has to start over. In fact, experience finds that truly it is a two-worker job to solve this puzzle.
Another shortcoming is that, if during use any of these springs gets deformed through mishap, it is virtually impossible for the customer-owners of the hammer tacker to repair the hammer tacker like new because of the challenge of re-tuning the springs. In fact, the assignee hereof has not really been any more successful at re-tuning springs deformed in the field than customer-owners. Indeed, repairing a broke-down hammer tacker with replacement parts re-encounters a shortcoming described above, namely, that there is virtually no uniformity between copies of the same part, ie., replacement parts. It often happens that after a replacement part is installed, the springs of the hammer tacker under-repair still require individual attention and tuning so that the package of springs as a whole works in concert as designed. For example, perhaps the piston will not return to its fully retracted position, and in consequence the ram's impulse surface will not clear the heads of the tacks in the strip. Without clearance, the tack strip will not advance, the rocker-arm/pawl linkage might stay caught in a strained position. An ill-advised attempt of solving this situation is to whack the hammer tacker as it is intended to be used, except to see if that might shake things loose. The reason that this is ill-advised is that, it risks damaging or in other words deforming any of the delicate springs/linkages. As an aside, the part most vulnerable to damage is the rocker-arm/pawl linkage.
Over the time that was spent refining this thread of designs (eg., the ones involving the double parallelogram spring and the reach-around pawl), it turned out that one attempt to solve a set of shortcomings tended to birth a different set of shortcomings. For example, in order to ensure that the ram's impulse surface clears the plane of the tack heads in the strip, the double parallelogram spring has evolved to provide a substantial force against the piston to keep it steady in its retracted or rest position, as between whacks. However, what also happens is that a substantial pre-load is built into the hammer tacker. The piston is forced so tight against its rest stop that it requires a worker to work that much harder on each whack, a fraction of which is waste just to overcome the resting force. Needless to say, this speeds up worker fatigue and detracts from worker efficiency.
FIGS. 4 through 6 are a series of views comparable to FIGS. 8c, 6a and 7a, respectively, in U.S. Pat. No. 5,927,922. That is, FIG. 4 hereof shows a collated strip of tacks in accordance with the prior art, wherein the direction of feed or procession of the strip through the hammer tacker 525 would be right to left in the view. FIG. 5 shows a single tack 520 in isolation. FIG. 6 is a bottom plan view of FIG. 4. The noteworthy aspect of FIGS. 4 and/or 6 is that, when tacks 520 are collated in the strip 570 according to the prior art, there is virtually no aperture left between the leading edge 571 of a tack head of a succeeding tack (eg., 520−1) and the leading edge of the head slot (eg., 568) in its preceding neighbor (eg., 520). This matter will be more particularly dealt with below.
What is needed is an improvement which overcomes various ones of the above-described shortcomings.
It is an object of the invention to eliminate where possible custom design springs in favor of readily available, off-the-shelf parts.
It is an alternative object of the invention to eliminate various heat-treatment steps during fabrication of the improved hammer tacker, it being presumed that the majority of required/advised heat treatments will have already been taken care of by the OEMs of such off-the-shelf parts.
It is an additional object of the invention to impose much closer dimensional tolerances on the springs because of simpler designs which are achieved by simply trimming such off-the-shelf stock to size or, in other words, eliminate overly-complicated spring designs achieved by layout on flat stock, formation into convoluted shapes, heat treatment to render the material serviceable again as a spring component, and then re-tuning the component to compensate for distortions brought on by the heat treatment.
A number of additional features and objects will be apparent in connection with the following discussion of the preferred embodiments and examples with reference to the drawings.